1. Field of the Invention
The present invention relates to a rolling bearing such as a roller bearing equipped with a spacer for installation and to a method for installing this rolling bearing, and, in particular, to a rolling bearing utilized in the assembly of a cam follower incorporated, for example, in a valve drive mechanism of an engine.
2. Description of the Prior Art
Conventionally, in a reciprocating piston engine used, for example, to propel an automobile, with the exception of certain two-cycle engines, intake and exhaust valves are provided which open and close in synchronism with the rotation of a crank shaft.
Devices of various configurations exist as a valve drive mechanism for driving these intake and exhaust valves. For example, in the SOHC type shown in FIG. 11, an intake valve 4 and an exhaust valve 5 are reciprocally driven through a pair of rocker arms 3 by a single camshaft 2 rotating at one half the speed of a crankshaft 1 (in the case of a 4-cycle engine). A pair of cams 6 secured to the camshaft 2 which rotates in synchronism with the crankshaft 1 slidingly contact the end sections of the rocker arms 3 and reciprocatingly drive an intake valve 4 and an exhaust valve 5.
In recent years, a rotating cam follower device which rotates along with the rotation of the cams 6 has been provided between the opposing parts, for example between the cam 6 and the rocker arm 3. This cam follower reduces the frictional forces between the peripheral faces of the cams 6 and the opposing members such as the rocker arms 8, the push rods (in an OHV type engine), the valves (in some DOHC-type engines), and the like, when the engine is running. This is designed to reduce the fuel consumption ratio when the engine is running.
This type of cam follower device is illustrated in FIG. 12 and FIG. 13. A pair of first and second support wall sections 7 are provided at one end of the rocker arms 3 with a space therebetween to support between them a part which opposes the cam 6. Each end of a shaft 8 is securely supported by one of the pair of support wall sections 7. A roller bearing comprising a plurality of rollers 9 and a short, cylindrical outer ring 10 is provided around the shaft 8. The outer peripheral surface of the outer ring 10 contacts the outer peripheral surface of the cam 6, so that this outer ring 10 rotates around the shaft 8 with the rotation of the cam 6.
By the provision of the roller bearing with this type of outer ring 10, the friction between the cam 6 and the parts which oppose the cam 6, such as the rocker arm 3 and the like is converted from sliding friction to rotational friction, thus reducing the fuel consumption ratio.
When installing the roller bearing between the two support wall sections 7 of the cam follower device described above, the rollers 9 provided inside the outer ring 10 must be maintained in a state where they will not become detached from the inner peripheral surface of the outer ring 10.
When the rollers 9 of the roller bearing are shipped from the factory, they are lightly attached to the inner peripheral surface of the outer ring 10 by a coating of grease. However, it is possible for some of the rollers 9 to become separated from the inner peripheral surface of the outer ring 10 due to vibration during transportation or impact during the installing operation, or the like.
If the rollers 9 which become separated from the inner peripheral surface of the outer ring 10 are completely detached from the inner peripheral surface of the outer ring 10, the load carried by the roller bearing is decreased as the number of rollers is reduced. Therefore, the life expectancy of the cam follower device is reduced. In addition, if the rollers 9 separated from the inner peripheral surface of the outer ring 10 remain inside the outer ring 10, these remaining rollers 9 become an obstacle to the insertion of the shaft 8, so that the cam follower device cannot be assembled.
As conventional technology to eliminate this type of inconvenience, the technology as disclosed in Japanese Laid Open U.M. Patents Nos. S64-36603 and S64-36604 is known. In this conventional technology, a spacer is further provided inside the rollers 9 within the outer ring 10. Prior to installing the roller bearing, the rollers 9 are secured by this spacer so that they do not separate from the inner peripheral surface of the outer ring 10. Then, as the shaft 8 is inserted into the space defined by the rollers 9, the spacer is pushed out from this space.
Commonly known shapes for the spacer to be installed inside the rollers 9 are shown in FIG. 14 to FIG. 17. The spacer 11 illustrated in FIG. 14 and FIG. 15 for preventing the detachment of the rollers q resembles a spacer for preventing the separation of a split inner ring described in "Compilation of Commonly Known and Conventional Technology" published by the Japanese Patent Office on Dec. 28, 1973. The spacer 11 of a synthetic resin such as nylon is formed in a cylindrical member With a notch or cutout formed in one part of the member, so that the outer diameter of the member is compressed elastically. Another type of spacer 12 shown in FIG. 16 is disclosed in US Patent No. 4166660. The spacer 12 is a metal plate spring formed in a W-shape.
Each of the spacers 11, 12 formed as described above is installed inside the space defined by the rollers 9 mounted inside the outer ring 10 and supports the rollers 9 from inside to prevent them from becoming detached from the inner peripheral surface of the outer ring 10 as a result of vibration during transportation of the roller bearing or from impact during the installing operation, or the like.
To perform the installing operation, the roller bearing comprising the outer ring 10 and the rollers q is inserted between the pair of support wall sections 7 formed at the ends of the rocker arms 3, with the spacer 11 or the spacer 12 still placed in the space defined by the rollers 9. The shaft 8 for supporting the roller bearing is then inserted from the outside (the left side in FIG. 14) into a first through-hole 13a formed in the first support wall section 7 (the left wall section in FIG. 14). Next, the leading end of the shaft 8 is passed through the space defined by the rollers 9 of the roller bearing, and is inserted into a second through-hole 13b formed in the second support wall section 7 (the right wall section in FIG. 14).
The insertion of the shaft 8 causes the spacer 11 or the spacer 12 to be pushed out of the space defined by the rollers 9 to be ejected from the second through-hole 13b formed in the second support wall section 7 for recovery.
In the configuration shown in FIG. 14, the inner diameter of the first through-hole 13a into which the shaft s is first inserted (the left side in FIG. 14) is slightly larger than the outer diameter of the shaft 8. Because of this, the occurrence of damage at the middle section of the outer peripheral surface of the shaft 8 which may contact the rollers 9 is prevented. At the same time, the inner diameter r of the second through-hole 13b on the leading side in the direction of shaft insertion is slightly smaller than the outer diameter of the shaft 8. As a result, after the insertion of the shaft 8 is completed, even before the two ends of the shaft 8 are crimped for edge expansion, the positional relationship of the shaft 8 and the rocker arm 3 cannot be shifted.
However, the efficiency of the installing operation is not necessarily good when the roller bearing is installed using the spacers 11, 12 with the shapes described above.
For example, in the case of the spacer 11 shown in FIG. 14 and FIG. 15, the outer peripheral edge of the leading end of the spacer 11 (the right end in FIG. 14) is apt to strike the inner peripheral edge of the second through-hole 13b. If this occurs, the spacer 11 cannot be extracted from the space defined by the rollers 9, so the insertion of the shaft 8 does not proceed smoothly. This causes the installing operation for the roller bearing to worsen.
In the publication "Compilation of Commonly Known and Conventional Technology", the chamfering of the outer peripheral edge of both ends of the spacer has been documented. However, when the thickness of the spacer is reduced to the point where the outer diameter of the spacer 11 can easily reduced or deformed, such a thin spacer results in insufficient chamfering.
In addition, one or some of the rollers 9 can drop into the notch or cutout formed in part of the cylindrical member so that it is possible for this roller or these rollers 9 to project to the inside more than the other rollers 9. In such a case, the roller 9 which has fallen into the notch or cutout hinders the insertion of the shaft 8.
Accordingly, the spacer 11 shown in FIG. 14 and FIG. 16, as recorded in "Compilation of Commonly Known and Conventional Technology" is satisfactory for preventing separation of the inner ring, but is not necessarily suitable for supporting the rollers 9. In particular, in the case where rollers with a small outer diameter (needles) are used, the rollers 9 tend to fall into the notch or cutout very easily, which tends to be a problem.
With the spacer 12 formed from a metal plate spring as shown in FIG. 16, the operation to mount the spacer 12 inside the rollers 9 is troublesome. In addition, there is concern that the roller bearing will deteriorate because of rusting of the metal plate spring from which the spacer 12 is formed. Also, because it is difficult to use the spacer 12 repeatedly because of the loss of spring force in the metal plate spring, an increase in the cost of installing the roller bearing is unavoidable.
Consideration has been given to the use of a barrel-shaped spacer 14 as shown in FIG. 17. The barrel-shaped spacer 14 has a diameter h of the outer periphery at each end which is considerably smaller than the inner diameter r of the second through-hole 13b (r&gt;h) as shown in FIG. 14. As a result, the ends of the spacer 14 can be smoothly fed into the second through-hole 13b.
However, when the entire outer peripheral surface of the simple barrel-shaped spacer 14 is spherical, even when the spacer 14 has been inserted into the space defined by the rollers 9, this spacer 14 tends to change position from a rocking or oscillating motion around the contact parts of the rollers 9. If this positional change becomes large, the end surface of the spacer 14 hits against the inner peripheral edge section of the second through-hole 13b, so that it is very difficult to extract the spacer 14 from the space defined by the rollers 9.